Alderamin, designated as Alpha Cephei, is a second magnitude star situated in the constellation of Cepheus, near the northern pole.
Key Facts & Summary
- Alderamin is quite close to us, situated at a distance of around 49 light-years / 15 parsecs away from the Sun
- Alderamin is a white class A star, evolving off the main sequence into a subgiant of spectral type A8Vn.
- Alderamin has an apparent magnitude of 2.5 and an absolute magnitude of 1.57. This star is also a suspected Delta Scuti variable type of star.
- This means that Alderamin has brightness variations, of around 0.06 magnitudes.
- Alderamin has a radial velocity of -10 kilometers / -6.2 miles per second.
- The surface gravity on Alderamin has been estimated at around 3,99 cgs.
- Alderamin has 1.74 solar masses, and when it comes to its radius, 2.3 solar radii. It is thus around 4 times bigger than our Sun.
- The average surface temperature on Alderamin is about 7,740 K, hotter than our Sun.
- Alderamin is around 17 times brighter than our Sun.
- Alderamin is a very fast-spinning star, having a rotational velocity of around 246 km / 152.8 mi per second.
- With such a rotational speed, Alderamin completes one revolution in around 12 hours.
- Alderamin is also known to emit X-rays, similar to our Sun, which along with other indicators suggests the existence of considerable magnetic activity – this is something unexpected for a fast rotator, though not unusual.
- The exact age of Alderamin is still being debated, however, the star’s next evolution phase is most likely a red giant.
- Alderamin is located near the celestial north pole, it periodically comes within 3 degrees of being a pole star, it will hold this title in 7500 CE.
Alderamin is the brightest star in the constellation of Cepheus, thus it has the designation Alpha Cephei. The star’s name comes from Arabic “al-dhira-al-yamin”, and it translates to “the right arm”.
The phrase was contracted into “Al Deraimin” in the 1521 Alfonsine Tables and eventually became Alderamin. This name was officially approved by the IAU in 2016.
Alderamin formed millions of years ago from an interstellar medium of dust and gas. Gravity pulled the swirling gas and dust together, and when it reached the right temperature, Alderamin was born.
Alderamin is quite an important star since it is relatively close to us, and since it is located near the north celestial pole, it takes turns with other stars in becoming the north pole star, used for navigation.
Distance, Size, and Mass
Alderamin is located at around 49 light-years / 15 parsecs away from the Sun. It is visible to the naked eye under the right conditions.
Alderamin is much bigger than our Sun, having 2.3 solar radii, or 230% of the Sun’s radius, and around 1.74 solar masses, or 174% of our Sun’s mass. Alderamin is around four times bigger than our Sun.
Alderamin is a white main-sequence star of spectral type A8Vn. It is in the process of evolving away from the main sequence and become a subgiant, and eventually a red giant.
Alderamin has an effective temperature of around 7,740 K, it is thus 1.3 times hotter than our Sun, and it is around 17 times brighter than our Sun.
Alderamin is quite a fast-spinning star, with an estimated rotational velocity of around 246 km / 152.8 mi per second. This means that Alderamin completes one revolution in 12 hours, while our Sun does so in almost a month.
Alderamin is also a suspected Delta Scuti variable, showing brightness variations of around 0.06 magnitudes. Its apparent magnitude is 2.5, thus it is visible to the naked eye, while its absolute magnitude is 1.57.
Delta Scuti variable stars display fluctuations in brightness as a result of both radial and non-radial pulsations of their surface. Alderamin is also a source of X-ray emissions, indicating significant magnetic activity, which is not typical for rapidly rotating stars.
Alderamin is one of the stars that act as indicators of true north and take their turn being the North Star due to the precession of the equinoxes.
The current north star is Polaris. The precession cycle lasts for around 25,770 years and Alderamin is among the visible stars that come within a few degrees of the pole and mark the true north.
Alderamin comes within 3 degrees of the north celestial pole, and this means that it is a less accurate indicator of the true north than Polaris, since Polaris comes within 0.05 degrees to the pole.
Alderamin was the north star in the year 18,000 BCE, and it will become again in around 7500 CE.
Alderamin / Alpha Cephei is located in the constellation of Cepheus, being the brightest star in the constellation. Cepheus is among the Greek constellations first cataloged by Ptolemy in the 2nd century CE.
Alderamin is quite easy to spot since it is located in the same area of sky as the bright W asterism formed by the brightest stars of Cassiopeia constellation.
An imaginary line extended from Schedar through Caph leads directly towards Alderamin. Cepheus is a relatively faint constellation, however, its brightest star Alderamin, stands out.
Since Alderamin is located near the north celestial pole, it is invisible to most southern observers. Alderamin can be seen north of latitude 27S and is circumpolar.
The constellation of Cepheus contains many notable stars such as Delta Cephei, the prototype for Cepheid variables, Beta Cephei, the prototype for Beta Cephei variables, the red supergiants Mu Cephei, and VV Cephei A, both among the largest known stars, the binary star Omicron Cephei, and the multiple star system Xi Cephei.
Other deep-sky objects in the constellation of Cepheus include the Fireworks Galaxy – NGC 6946 – named for the regular supernovae explosions, Alderamin is close to it, the open cluster NGC 188, the star-forming nebula NGC 7538, the Cave Nebula, the Wizard Nebula, and the Iris Nebula.
Alderamin is evolving off the main sequence into a subgiant, probably on its way to becoming a red giant as its hydrogen supply runs low. It will expand its radius several times, dwarfing the size of our Sun several times.
Alderamin has a bright future, as in 7500 CE it will become the north pole star once again. It will be succeeded, however, by the considerably brighter star Deneb in Cygnus, the 19th brightest star in the sky.
Did you know?
- The Chinese know Alderamin as the Fifth Star of the Celestial Hook, the Celestial Hook is a Chinese asterism formed by Alderamin and several other stars.
- Timurid astronomer Ulugh Beg saw Alderamin, Beta Cephei, and Eta Cephei, as the “al-Kawakib al-Firq” – “the stars of the flock”.
- USS Alderamin (AK-116) was a U.S Navy Crater class cargo ship named after the star.
- Alderamin is circumpolar throughout Europe, northern Asia, Canada, and American cities as far south as San Diego.